1. Field of the Invention
This invention relates to an integrated control system for a gas turbine engine and, more particularly, to an apparatus for interfacing between a primary control means and a backup control means in such control system, for engine deceleration rate limiting in such a control system, or both.
2. Description of the Prior Art
Full authority electronic control systems for gas turbine engines provide a number of significant advantages over conventional hydromechanical control systems. However, since full authority electronic control systems are only advancing to what might be termed a first generation level, confidence in the reliability of such electronic controls has not attained the level generally associated with the hydromechanical systems which have been in use for many years in highly refined configurations. Consequently, it is advisable to complement the electronic control system with a secondary or backup hydromechanical control system which will assure continued operation of the engine in the event the primary electrical control system exhibits a malfunction or a failure.
In a gas turbine control system having such a backup capability, it is necessary to have compatibility between the primary electronic control system and the backup hydromechanical control. In other words, the backup system must not interfere with the primary system when the latter is in control of the engine and vice versa.
It is also desirable to have a control system in which both the primary and the backup control systems are fully operable in controlling the engine during normal operation. In addition, it is necessary to have a control system in which, upon a failure of the primary electronic control system, transfer of control is accomplished in a controlled and orderly manner in which step-type changes and immediate alterations in engine operation are avoided.
Although the control system disclosed in the aforementioned U.S. Pat. No. 4,137,707 is fully capable of achieving these goals, it does so at the expense of utilizing sophisticated additional components which unnecessarily increase the weight, complexity and cost of the control system. The present invention overcomes these drawbacks by providing a simplified interfacing system in which existing control system components are adapted to automatically perform the requisite transfer functions without any significant increase in system weight, complexity or cost.